1. Field of the Invention
This invention relates to a method of producing a ceramic honeycomb filter and a film perforating device therefor. More particularly, the invention relates to a method of producing a ceramic honeycomb filter by using a film applied to one or both end surfaces of a ceramic honeycomb body for selectively sealing open ends of throughholes thereof, and also relates to a film perforating device for selectively boring holes on the above-mentioned film at positions corresponding to selected open ends of the throughholes to be sealed.
2. Description of the Prior Art
To purify exhaust gas from an internal combustion engine, a ceramic honeycomb filter has been used, and the said filter comprises a ceramic honeycomb body made of porous ceramic material and having a plurality of throughholes extending therethrough. Some of the throughholes in such ceramic honeycomb body of the filter are sealed by suitable sealant at one side ends thereof, while the remaining throughholes thereof are sealed by suitable sealant at the opposite ends thereof, so that the partition walls between the adjacent throughholes act as filtering layers.
For the production of such ceramic honeycomb fitler, a method has been proposed by U.S. Pat. No. 4,293,357, which comprises steps of attaching a film onto that open end surface of an extruded ceramic honeycomb body which is to be selectively sealed, perforating holes on the film at positions corresponding to desired end openings of throughholes of the honeycomb body, filling a sealant into the honeycomb body through the thus perforated holes of the film, and firing the honeycomb body at 800.degree.-1,400.degree. C. so as to burn away the film while sintering the sealant for sealing the desired open ends of the selected throughholes of the ceramic honeycomb body.
However, the proposed method has a shortcoming in that each of the throughholes of the extruded ceramic honeycomb body has strain or deformation caused during the extrusion or caused by firing shrinkage, and such a strain makes it very difficult to properly perforate the film at the open end of the ceramic honeycomb body at a high efficiency. In fact, there is no film perforating device available for efficiently perforating the above-mentioned film in producing the ceramic honeycomb filter.